That vertebrates produce otoacoustic emissions and detect sounds near Brownian motion amplitudes suggests that the auditory system contains an active amplifier and filter. This project examines how hair cells contribute to this active process by measuring the relationship of mechanical tuning and amplification in the hair bundles of auditory hair cells to the overall spectral tuning in the end organ. Using patch clamp recordings and photometric measures of hair bundle movement, proposed research will test whether hair bundles tune mechano-electric transduction, amplify their mechanical response at certain frequencies and receive feedback from the electrical filter of hair cells' basolateral membrane. The test preparation will be the hair cells of the turtle auditory papilla, which are known to contain hair bundles that oscillate near the characteristic frequency of the cells. Although this project should be of interest to a broad audience in auditory neuroscience, particular interest should come from those studying active processing in mammals, where hair bundles potentially play a role in the tuning of outer hair cell motility.